LED and OLED devices become more and more popular as lighting elements not only in the technical application fields but also in private home application fields. Irrespetive of the application, it is always desired that the LED/OLED devices radiate light with the same intensity even over long periods. Due to aging effects, particularly with OLED devices, the light output decreases without compensation. Therefore, it is necessary to compensate for the aging so as to keep the light output constant.
Further, it is also desired that the driver circuit for supplying power to the LED/OLED devices may be operated to assure constant light output independent of the size of the LED/OLED device. For example, OLED luminaries with a different number of tiles require the adjustment of the OLED current. In other words, the driver circuit should be scalable.
For convenient use in the home environment, it is desired to carry out these operations automatically. The user should not have to perform any control or adjusting.
Prior art techniques have utilized simple static measurements delivering only one parameter for determining a status or condition of a LED/OLED device for compensating aging, etc. This parameter is, for example, forward voltage or slope of the IV-curve or an impedance value.
Static measurements are prone to electrical noise and interference under field conditions. To reduce interference during parameter detection filtering can be used. This, however, is quite expensive because the size of passive components scale with frequency and are most expensive for DC. Moreover, static measurements derive differential characteristics from the difference of two (or more) large signal operating points. A very unreliable procedure.
Further limitations and issues of prior art appear when more than one OLED parameter has to be determined such as the size of an OLED. To determine the size with static measurements parameters of the non-linear IV-characteristic will be used as a measure. Assuming a specific IV-characteristici=a·(v−vf)b 
the gain factor “a” is a measure for the size of the OLED for a given vf, b. In the following, two examples will be given to determine the gain factor “a”, wherein in the first case vf and b are known, and in the second case vf is unknown as well.
To determine gain “a”, the OLED is driven with a test current Im, which must be low enough to avoid a destruction of the OLED. Then the voltage across the OLED vm is measured. Now the gain can be calculated:
  a  =            i      m                      (                              v            m                    -                      v            f                          )            b      
This method works quite easy, requires, however, the knowledge of the OLED characteristic b and the forward voltage vf. It is, however, the forward voltage which depends strongly on the temperature, so that it is necessary for an increased accuracy to treat vf as unknown as well, so that an additional measurement has to be done.
In the second case, there are two unknowns, so that at least two measurements have to be made:i1=a·(v1−vf)b i2=a·(v2−vf)b 
Solving these two equations for vf and a gives:
      a    =                            [                                                    v                2                            -                              v                1                                                                                      (                                                            i                      2                                                              i                      1                                                        )                                                  1                  b                                            -              1                                ]                          -          b                    ·              i        1                        v      f        =                            i          2                      1            b                          ·                                            v              1                        -                          v              2                                                          i              2                              1                b                                      -                          i              1                              1                b                                                        +              v        2            
It is obvious that this method can be extended to many more OLED parameters in order to characterize the various OLEDs of a certain family. The problem is, however, that the underlying equations become non-linear. The form of equations itself of device dependent so that there is no simple standardized procedure to determine OLEDs' parameters. In effect, static measurements are typically limited to determine one single parameter. Moreover, static measurements are prone to electrical noise and interference. Filtering is quite expensive because the size of passive components scale with frequency and are most expensive for DC. Moreover, static measurements derive differential characteristics from the difference of two (or more) large signal operating points. A numerically noisy procedure.